Multispectral optical inspection system for testing solar cells spectral perfomance

Abstract

A low-cost multi-spectral optical system for inspecting the spectral performance of photovoltaic solar cells (10) in the field, and / or during the production phase. It comprises a modulated laser sources (14), used for inducing a similar photocurrent in the inspected cell (10) as a precise metric of the efficiency. It comprises also a receiving module (20) connected in series to the cell. It provides simplicity, reliability, ease of use, fast response, and high-precision diagnosis of solar cells troubleshooting with / without load engagement, at full-sun illumination and / or full-darkness, which fulfills the requirements of industrial quality control and / or large sites preventive maintenance.

Description

[0001] MULTISPECTRAL OPTICAL INSPECTION SYSTEM FOR TESTING SOLAR CELLS SPECTRAL PERFOMANCE FIELD OF INVENTION

[0001] The present invention is an optical system, for inspecting the spectral performance of photovoltaic solar cell. BACKGROUND OF THE INVENTION

[0002] Since the discovery of photovoltaic effect by Becquerel in 1839, solar cells concept has been slowly developed, until the invention of the first reliable silicon photovoltaic cell in 1950 by Bell Laboratories, where its first application in powering satellites and spacecraft without the need for fuel, but after the early seventeen’s energy crisis, research institutions began to focus on improving the efficiency and reducing the cost of solar cells, until the 21stcentury when manufacturing processes has achieved a lot of improvements by developing new materials and high efficiency designs that increased the durability and reduced the production costs of the solar panels, consequently, the market for solar energy expanded rapidly, since solar panels became increasingly affordable and accessible to businesses, homeowners and utilities, leading to the large scale adoption of solar power as a renewable energy source.

[0003] Most solar cells consist of several basic components such as a heavily doped semiconductor material, an antireflection coating, a front contact grid made of transparent conductive material, a back contact conductive metallic material, bus-bars, interconnects, a bypass diodes to mitigate the effect of shading and a transparent tempered glass or plastic encapsulation, these components are integrated to convert sunlight into electricity by the photovoltaic effect.

[0004] Unfortunately, solar panels are subjected to troubleshooting and efficiency deterioration during their service life, due to several factors including, light-induced semiconductor degradation, high temperature efficiency loss, humidity and moisture corrosion, mechanical stresses and micro-cracks, ultra-violet radiation coating degradation, encapsulation degradation, chemical contamination recombination losses and potential induced degradation.

[0005] Several methods has been adopted to inspect solar panels performance such as visual inspection of physical damages, inverter output monitoring, remote monitoring of voltage and current, thermal imaging of hot spots, and historical performance data analysis, however, none of these methods can provide a precise diagnosis and / or localization for the real damage at the semiconductor junction level, unles ଶs followed by sophisticated efficiency tests such as the standard reported conditions test under 1^^^^ / ^^ irradiance (ASTM E948), including current-voltage curve tracing, the maximum power point, the energy conversion efficiency percent, the fill factor, beside the spectral responsivity and spectral mismatch measurements under variable wavelength irradiance (ASTM E2236, ASTM E1036), and finally the external / internal quantum efficiency (ASTM E1021).

[0006] Most of the previous methods depend on direct current measurements, only few methods perform very low frequency synchronous measurements (such as ASTM E1021) and does consider neither the time nor the frequency response of the solar cell, despite of their great importance in analyzing the change of conductance and / or capacitance and / or inductance, that are considered as a very certain structural and / or functional indices for the semiconductor junction performance.

[0007] The present invention merges between accurate time and / or frequency domain measurements, and spectral response, in order to inspect the spectral performance of solar cells, and to determine their quantum efficiencies and spectral performances, at full-sun illumination and / or complete darkness, with and / or without load engagement, providing mobility, low-cost, simplicity, reliability, ease of use, fast response, and high-precision diagnosis of troubleshooting.

[0008] The present invention fulfills the requirements of industrial quality control to test solar cells, and solar panels during their production, also it fulfills the requirements of large photovoltaic solar fields preventive maintenance. SUMMARY OF THE INVENTION

[0009] According to the present invention a novel category of electro-optical devices has been introduced to solar cells testing. In this category, the concept of direct current measurements is replaced by the concept of alternating current measurements, merging between time and / or frequency response, and spectral response measurements, in order to inspect the true performance of solar cells, to reveal the nature of troubleshooting.

[0010] There are many factors that interplay to determine the response of a solar cell to an impulse of light, where the most important are classified into intrinsic and extrinsic factors.

[0011] To obtain the intrinsic frequency response of a solar cell, let us assume that ^^ is the time, ^^^^and ^^^^are the transit time of electrons and of holes through the entire depletion region, so that the intrinsic impulse response, is given by the equation: ^^ ^^^(^^)^^ష^^ൗ^^^^^^ ^^ൗ ^^^^^^^ = −^^^^^^− ^^^^^^(1) and therefore, if ^^^^is the optical ^^ the solar cell is obtained by applying ^^^^^^^^(^^^^) = − ^^^^ା^^^^^^^^^^^^^^−^^^^ା^^^^^^^^^^^^^^(2)

[0012] To obtain the extrinsic semiconductor junction working in an equivalent circuit comprising a junction resistance ^^, a shunt diffusion capacitance ^^^^, a shunt junction capacitance ^^, and an external load series resistance ^^^^. This equivalent circuit acts as a low pass filter, where the extrinsic frequency response is given by the equation: ^^^^^^^^(^^^^) =^^ (^^ା^^^^)ା^^^^^^^^^^(^^ା^^^^)(^^^^^^)≈ ^^ ^^ା^^^^^^^^^^^^^^^^ (3)

[0013] To obtain the of wavelength ^^ with of absorption coefficient ^^(^^), ^^(^^) =^^^^ି^^(^ )^^^^^^(^^)൫^^ − ^^ ^ ^^൯൫^^ − ^^(^^)൯ (4)where ^^ is elementary charge ^^ ^^ and ^^ is the velocity of light. cell, the responsivity of the solar cell at a specific wavele th, is given by the equation: ^^(^^) =^^(^^) ^^(^^)= ^^(^^)^^^^ ^^^^= ^^(^^)^^ ^^^^^^^^ (5)

[0014] To merge between the that the same beam of resulting photocurrent is given by the equation: ^^(^^, ^^^) = ^^(^^, ^^ )^^(^^)^^ (^^ )^^ (^^ ) (6)

[0015] Since the equivalent circuit acts a^s a low pa^s^s filter t^h^^e^^^n ^^^^(^^,^^^^^^^^^^) te^^nds to ^^(^^) as ^^^^ tends to zerosuch that: ^^^^^^^^^^→ ^^ ^^(^^, ^^^^) = ^^^^^^^^(^^, ^^^^) = ^^(^^) (7)so that, ^^(^^) = ^^^^^^^^(^^, ^^^^) ^^^^^^ ^^^^ ^^^^ = ^^^^^^^^^^ ^^^^(8)

[0016] the spectral efficiency of the semiconductor material and the integral of ideal quantum efficiency over the same working wavelength ran ^^^^^^ ∫^^g ^^e, such that: ^^^^ ^^(^^)^^^^^^^^^^^^ ^^^^^^^^^^ ^^^^^^ ^^^^^^^^^^ ^^^^ ^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^ (9) where ^^^^and ^^^^represent the shortest wavelength and the longest wavelength at which the quantum efficiency cuts off, and considered as a characteristic parameters for a specific semiconductor material, that ^^^^^^^^^^^^(^൫^^)^= ^^, equation (9) is approximated by the expression:^^ష^^^^൯^^^^^^^^ ≈^^^^(^^^^)ା(^^^^ି^^^^)^^(^^^^)ା(^^^^ି^^^^)^^(^^^^)ା⋯ା(^^^^ି^^^^ష^^)^^(^^^^ష^^)ା൫^^^^ష^^ ൯^^^^(^^^^)(^^^^ି^^^^) (10)

[0017] it is a −^^^^^^^^ ^^^^^^^^^^ ^^^^^^ ^^^^^^^^ ^^^^ ^^^^^^^^^^ ^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^let ^^(^^) is the external quantum efficiency los ( )^^^^^^ ≈൫^^s which equals 1 − ^^ ^^ , so that:^^ష^^^^൯^^ ^^(^^^^)ା(^^^^ି^^^^)^^(^^^^)ା(^^^^ି^^^^)^^(^^^^)ା⋯ା(^^^^ି^^^^ష^^)^^(^^^^ష^^)ା൫^^^^ష^^^^൯^^ ^^(^^^^) (^^^^ି^^^^) (12)

[0018] responses to the spectral to append the energy efficiency (^^) and the current spectral mismatch factor (^^^^^^), since half of the solar energy is concentrated is the ultraviolet-visible range and the other half is concentrated in the near infrared range, while only one percent of this energy is left for the mid / far infrared range, and help in the evaluation of true photonic energy conversion efficiency.

[0019] Consequently, the present invention is capable of inspecting the spectral performance of photovoltaic solar cells. It comprises a number ^^ of laser sources with selected different wavelengths andpower (^^) , energized sequentially, chopped with a carrier frequency ^^requency ^^ ^ , and modulated by a lowf ^^, for inducing a similar time variant photocurrent ^^(^^, ^^^^) in th^e inspected cell, of frequency^^^^^^. It comprises also, a synchronized receiving module, connected in series to the cell through an AC / DC splitter, this module acts as lock-in amplifier that tracks the photocurrent ^^ ^^ signal in presenceof noise, and convert it to a voltage signal ^^(^^, ^^ ), with frequency ^^ . This si(gn)al is delivered to acontrol unit which is preprogrammed with the^^necessary paramet^e^rs, to calculate ^^^^^^^(^^, ^^ ) ,^^ (^^, ^^ ), ^^^^^^ and ^^^^^^, while sweeping ^^ in a transmitter unit, a ^ ^^^^^^^^ ^^ ^^ nd selecting between the lasersources in a multispectral optical emitter unit to trace the Bode plots.

[0020] In light of the preceding introduction, the present invention allows for a comprehensive analysis of how a solar cell responds under different troubleshooting, as shown in table (1).

[0002] Table (1) Correlation between the troubleshooting and the obtained readings × × × × × × - × × ----

[0021] By adopting the present invention in maintenance and inspection operations, it will be possible to investigate both the spectral performance and the time variant electrical response of almost any type photovoltaic cells, such as, crystalline silicon, thin-film, perovskite, organic and multijunction solar cells.

[0022] The present invention reduces the size and the weight of the solar panels test facilities, providing mobility, simplicity and ease of use.

[0023] The present invention allows for testing the solar panel in presence of full-sun irradiation where most of the photo-carriers are contributing in the energy conversion process.

[0024] The present invention allows for testing the solar panel in full-darkness where some of the carriers are contributing in the dark current leakage process.

[0025] The present invention allows for testing the solar panel in presence of stray irradiation of artificial industrial lightings, where a portion of the photo-carriers are contributing in the time variant energy conversion process.

[0026] The present invention allows for tracing the Bode plots representing the electric frequency response of the inspected solar cell, at different wavelengths, and allows for tracing both the spectral responsivity and the external quantum efficiency curves of said cell.

[0027] The present invention introduces a new solar cell parameters which are the spectral performance factor ^^^^^^ and the spectral loss factor ^^^^^^, these factors append current efficiency metrics, improve troubleshooting inspection, and help in preventive maintenance of photovoltaic solar fields.

[0028] The present invention can be used in industrial quality control stage in solar panels factories, since testing beam can be either irradiating one solar cell element in the panel, or irradiating the whole panel.

[0029] The present invention can be used in industrial quality control stage in solar panels factories, since testing beam can be either irradiating one solar cell element in the panel, or irradiating the whole panel.

[0030] The present invention can be used in testing photo-detectors responsivity, and spectral performance.

[0031] The present invention, provides fast response, saves time and reduces the inspection run period to less than few seconds.

[0032] The present invention provides low-cost, reliability, and high-precision diagnosis of troubleshooting. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The present invention is explained more closely by means of different embodiments and with reference to the attached drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, the invention may admit to other equally effective embodiments.

[0034] FIG.1 illustrates the different elements contributing in a multispectral optical inspection system for testing solar cells spectral performance according to an embodiment of the present invention;

[0035] FIG.2a illustrates the functional block diagram of a synchronous receiver unit, in a multispectral optical inspection system for testing solar cells spectral performance, according to another embodiment of the present invention;

[0036] FIG.2b illustrates the functional block diagram of a control unit, in a multispectral optical inspection system for testing solar cells spectral performance, according to an embodiment of the present invention;

[0037] FIG.3a illustrates the functional block diagram of a transmitter unit, in a multispectral optical inspection system for testing solar cells spectral performance, according to an embodiment of the present invention;

[0038] FIG.3b illustrates the functional block diagram of a multispectral optical emitter unit, in a multispectral optical inspection system for testing solar cells spectral performance, according to another embodiment of the present invention.

[0039] FIG.4 illustrates the signals time diagram, in a multispectral optical inspection system for testing solar cells spectral performance, according to yet another embodiment of the present invention.

[0040] FIG.5 illustrates the Bode plot of the output signal, in a multispectral optical inspection system for testing solar cells spectral performance, according to another embodiment of the present invention.

[0041] FIG.6 illustrates the external quantum efficiency curve for a solar cell, in a multispectral optical inspection system for testing solar cells spectral performance, according to yet another embodiment of the present invention.

[0042] Drawings reference numerals 10 Photovoltaic solar panel 11 The sun 12Solar radiations 13 Laser beam 14 Multispectral optical emitter unit 15 Transmitter output power cable 16 Transmitter unit 17 Frequency sweep control cable 18 Control unit 19 Synchronous receiver output cable 20Synchronous receiver unit 21 High frequency photocurrent cable 22 High frequency power splitter 23Low resistance inductor 24 High frequency photocurrent pass capacitor 25 Solar panel output power cable26Electric load supply cable 27 Electric load Circuit ground Transmitter synchronization signal cable Input / Output interface Trans-conductance amplifier Band-pass filter Synchronous demodulator Phase shifter Low-pass filter Voltage follower Laser source address cable Voltage controlled oscillator Limiting amplifier Low frequency oscillator Mixer Power amplifier De-multiplexer (laser source selector) Plurality of laser source with different wavelengths and powers Optical collimator Input / output bus Main controller Analogue to digital converter Digital to analogue converter Normal frequency response of a solar cell at selected wavelengths Frequency response of an aged solar cell Frequency response of a defected solar cell External quantum efficiency curve of a solar cell Efficiency loss zone due to semiconductor rear surface photo-carriers recombination Efficiency loss zone due to surface reflection Efficiency loss zone due to semiconductor front surface photo-carriers recombination External quantum efficiency of a solar cell Maximum external quantum efficiency as a function of wavelength and carrierfrequency Wave length Longest wavelength where the quantum efficiency of the semiconductor cuts-off A specific wave length Shortest wavelength where the quantum efficiency of the semiconductor cuts-off Minimum external quantum efficiency loss as a function of wavelength and carrierfrequency Responsivity as a function of wavelength and carrier frequencyMaximum responsivity as a function of wavelength and carrier frequencyCarrier frequency Demodulated carrier frequency Modulation frequency Modulated carrier frequency Wavelength selection frequency Carrier sweep frequency Photocurrent as a function of wavelength and carrier frequencyMaximum photocurrent as a function of wavelength and carrier frequency ^^(^^) Optical Irradiation power as a function of wavelength ^^^^^^^^^^^(^^) Maximum optical Irradiation power as a function of wavelength ^Output voltage as a function of wavelength and carrier frequencyMaximum output voltage as a function of wavelength and carrier frequency〉 Average maximum output voltage as a function of wavelength and carrier frequency OF THE INVENTION to an embodiment of the current invention, figures 1 illustrates the basic components of a multispectral optical inspection system for testing solar cells spectral performance comprising, a solar panel under inspection (10) that receives sun (11) radiation (12), while being partially or completely irradiated by a modulated laser (13) emitted from a multispectral optical emitter unit (14), a transmitter unit (16), a control unit (18), a synchronous receiver unit (20), a high frequency power splitter (22), and an electric load (27) to consume the solar panel DC current.

[0044] According to the same embodiment of the current invention, the modulated laser beam (13) represents the AC component of the solar panel photocurrent, while the sun radiation (12) represents the DC component.

[0045] According to the same embodiment of the current invention, the AC component of the solar panel photocurrent, is separated using the high frequency power splitter (22), to feed synchronous receiver unit (20), that retrieves the modulated signal from the noise, in order to compare its amplitude to a reference value preprogrammed in the control unit (18), prior to efficiency calculation.

[0046] According to yet the same embodiment of the current invention, the control unit (18), controls both the transmitter unit (16) by changing the carrier frequency, and the multispectral optical emitter unit (14) by selecting between a plurality of different wavelength laser sources, such that after every carrier frequency sweep cycle a different laser source is selected, providing the frequency response of the irradiated area of the solar panel (10).

[0047] According to another embodiment of the current invention, figures 2a illustrates the functional block diagram of a synchronous receiver unit (20), comprising a trans-conductance amplifier (31) , that converts high frequency photocurrent into voltage signal with a gain of ^^, a band-pass filter (32) to reject all frequencies except that of the swept carrier band, a synchronous demodulator (33) that separates a low frequency modulation signal from the swept carrier, a phase shifter (34) that shifts transmitter signal 90 degrees to feed the synchronous demodulator, a low-pass filter (35) that rejects all high frequency components from the demodulator output signal leaving only the low frequency modulation signal, and a voltage follower (36) to isolate between the output of the low pass filter (36) and the next stage.

[0048] According to the same embodiment of the current invention, figures 2b illustrates the functional block diagram of a control unit (18), comprising an analogue to digital converter (48) that digitizes the low frequency modulation signal (19) in order to find its ratio relative to a preprogramed value saved in a main controller (47) prior to a spectral performance calculation program, an input / output bus (46) that connects both the entry keys and readout screen, with the main controller (47), and a digital to analogue converter that generates a staircase sweep voltage signal (17) prior to the next carrier generation stage.

[0049] According to a related embodiment of the current invention, figures 3a illustrates the functional block diagram of a transmitter unit (16), comprising a voltage controlled oscillator (38) cy in the range from 10ଷthat generates acarrier frequen − 10ହ^^^^ according to the sweep signal (17), followed by alimiting amplifier (39) feeding ଶ a mixer (41) that mixes the swept carrier frequency with a low frequency square wave in the range of 10 ^^^^, from low frequency oscillator (40) at modulation depth 100%, and a power amplifier (42) to prior to the next step.

[0050] According to the same embodiment of the current invention, figures 3a illustrates the functional block diagram of a multispectral optical emitter unit (14), comprising a demultiplexer (43) that selects between a plurality of laser source with different wavelengths (44) to feed it with modulated power signal (15) according to a control signal (37), and an optical collimator (45) that eases aiming the modulated laser (13) perpendicularly on the selected solar panel (10) area.

[0051] According to another embodiment of the current invention, figures 4 illustrates the time diagram of the different signals of the system, wherein a voltage signal ^^^^of frequency ^^^^sweeps a carrier frequency ^^^^to be modulated by amplitude via modulation signal of frequency ^^^^and modulation depth of 100%, this signal ^^ chops the output (13) of a sequentially selected laser source (44), among ources of different wa^^^s v^^e^lengths, via selection signal of frequency ^^ , such that ^^ > ^^ > ^^ > ^^^ > ^^ , ^^ > ^^^^ an ^^ ^^ ^ ^ ,^^ ^ ^^ ^^^^ ^^ ^^ ^^ d ^^^^ ≥ ^^^^^^ .

[0052] According to the same embodiment of the current invention, figures 4 illustrates the time diagram of the different signals of the system, wherein the modulated laser signal ^^(^^) induces photocurrent^^(^^, ^^ ) of small intensity in the photovoltaic cell (10), this current signal is amplified and converteg^e^ d intovolta signal ^^(^^, ^^ ) with suitable amplitude, then demodulated and filtered to a voltage signal〈 ^^^^(^^, ^^^^)〉 of a frequency ^^^^ , such that ^^^^ = ^^^^ .

[0053] According to another embodiment of the current invention, figures 5 illustrates a Bod plot traced by the control unit (18) which is preprogrammed with the necessary parameters, to calculate frequencyresponse which equals ^^(^^, ^^^^)⁄ ^^^^^^^^(^^, ^^^^) = 〈^^(^^, ^^^^)〉⁄ 〈^^^^^^^^(^^, ^^^^)〉 , while sweeping ^^^^ in atransmitter unit (14), and selecting sequentially between the laser sources, wherein the response at the selected wavelengths of a normal (50), aged (51) and defected (52) solar cell.

[0054] According to yet another embodiment of the current invention, figures 6 illustrates an external quantum efficiency curve (53) traced by the control unit (18) which is preprogrammed with the necessaryparameters, to calculate, the spectral maximum responsivity ^^ (^^, ^^ )at each selected wavelewhich equals to ^^^^^^^^(^^, ^^^^^^^^^^^^)〉⁄ ^^ × ^^(^^) , the external quan^t^ ngth,〈 u^^m^^eff^i^ciency ^^(^^) which equals to^^^^^^^^^^(^^, ^^^^) , the spectral performance factor ^^^^^^ and the spectral loss factor ^^^^^^ which൫^^^^ష^^^^൯^^(^^ )ା(^^ ି^^ )^^(^^ )ା(^^ ି^^ )^( ) ( ) ( )൫^^^^ష^^^^൯( ) approximately equal to ^^^^ ^^ ^^ ^^ ^^ ^^^ ^^^^ା⋯ା ^^^^ି^^^^ష^^^^ ^^^^ష^^ା ^^ ^^ ^^^^^^^^ , and ^^ − ^^^^^^respectively, represents the the absorption at zone zone (56) represents the efficiency loss due to semiconductor front surface photo-carriers recombination that reduces the absorption at short wavelengths.

[0055] According to the preceding description of the present invention, a prospective analysis of the solar cell troubleshoots, can be realized through the obtained system output parameters as previously shown in table (1).

[0056] In the present invention, if the low frequency oscillator (40) is replaced by a data source, and if the voltage controlled oscillator (38) is DC biased , while eliminating the transmitter synchronization signal cable (29) and modifying the synchronous receiver unit (20) to homodyne or heterodyne configuration, the illustrated system can be used as a long standoff half-duplex data link.

[0057] The scope of the invention shall be determined by the appended claims and their prospective legal equivalence, and not by the provided illustration example. SUMMARY, RAMIFICATIONAND SCOPE

[0058] From the preceding illustration, it will be seen that the described invention is a layout of a multispectral optical inspection system for testing solar cells spectral performance with a modulated light sources, used for inducing a similar photocurrent in the inspected cell as a precise metric of the efficiency. It comprises also a receiving module connected in series to the cell. It merges between accurate time and / or frequency domain measurements on one hand, and spectral response on the other hand, in order to inspect the performance of solar cells, and to determine their efficiencies at full-sun illumination and / or complete darkness, with and / or without load engagement, providing low-cost, simplicity, reliability, ease of use, fast response, and high-precision diagnosis of troubleshooting. Basing on the previous description, the scope of the invention shall not be limited on the given design example that is subject of changes by skilled artisans, but rather on the scientific methodology behind this embodiment.

Claims

CLAIMS What is claimed is:

1. A multispectral optical inspection system for testing solar cells spectral performance, said multispectral optical inspection system for testing solar cells spectral performance comprising: a multispectral optical emitter unit, wherein a plurality of laser sources with different wavelengths and powers, are connected to a demultiplexer to select between said sources, and an optical collimator to focus the laser beam on tested photovoltaic cell, a high frequency power splitter connecting between the output power terminal of said photovoltaic cell and a grounded load, providing high impedance to high frequency photocurrent between said photovoltaic cell and said grounded load, a very low resistance to direct current between said photovoltaic and said grounded load cell, and a very low output impedance to said high frequency photocurrent between said photovoltaic cell and the input of any possible amplification stage. a synchronous receiver unit with , wherein said high frequency photocurrent from said high frequency power splitter, is amplified by a trans-conductance amplifier and demodulated by synchronous detector, a control unit with input / output interface, wherein said demodulated high frequency photocurrent analogue voltage signal is converted into digital signal to be stored and processed by a main controlled that generates a sweep voltage signal and a sequential controls signal to select between said plurality of laser sources, a transmitter unit, wherein a modulated carrier high frequency signal swept by said sweep voltage, is synthetized to chop the output power of said selected laser source, and a reference carrier frequency is generated to feed said synchronous receiver unit, and wherein said multispectral optical inspection system for testing solar cells spectral performance is capable of acquiring the frequency response and the spectral response of said photovoltaic cell, to provide the spectral responsivity and the external quantum efficiency.

2. A multispectral optical inspection system for testing solar cells spectral performance, according to claim 1, wherein said laser irradiation is doubly chopped by a high frequency carrier and by a low frequency modulation such that said high frequency carrier is four times greater than said low frequency modulation.

3. A multispectral optical inspection system for testing solar cells spectral performance, according to claim 1, wherein the frequency said sweep voltage signal is two times greater than the frequency of said sequential controls signal.

4. A multispectral optical inspection system for testing solar cells spectral performance, according to claim 1, wherein the frequency said low frequency modulation signal is three times greater than the frequency of said sweep voltage signal.

5. A multispectral optical inspection system for testing solar cells spectral performance, according to claim 1, wherein the merge between time and / or frequency response, and spectral response in one measurement is used to provide the true performance of solar cells and to reveal the nature of troubleshooting by analyzing the obtained Bode plots.

6. A multispectral optical inspection system for testing solar cells spectral performance, according to claim 1, wherein the maximum said photocurrent magnitude over said frequency response of said solar cell at a specific wave length, represents its responsivity to said wavelength.

7. A multispectral optical inspection system for testing solar cells spectral performance, according to claim 1, wherein said high frequency power splitter, said synchronous receiver and / or said control unit and / or said transmitter unit work in homodyne mode, and / or in heterodyne mode, or works as a half- duplex and / or full duplex communication link beside being used as an inspection tool.

8. The method of spectral performance factor in solar cells efficiency testing, wherein, the ratio between the integral of external quantum efficiency of the semiconductor material and the integral of ideal quantum efficiency over the same working wavelength range is considered as energy conversion efficiency metric.

9. The method of spectral loss factor in solar cells efficiency testing, according to claim 8 wherein, one minus said ratio between the integral of external quantum efficiency of said semiconductor material andsaid integral of ideal quantum efficiency over said same working wavelength range is considered as energy conversion loss metric.

10. The use of a multispectral optical inspection system for testing solar cells spectral performance, according to claim 1, in testing and characterizing optical photodetectors.

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